Ornamental bulb



FIG. 1 is a front-left-top perspective view of an ornamental bulb, showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof. 

The ornamental design for an ornamental bulb, as shown and described. 